Assessing Changes in Adolescents' Sleep Characteristics and Dietary Quality in the START Study, a Natural Experiment on Delayed School Start Time Policies

Abstract

Background: Sleep duration, quality, and timing may influence dietary quality. In adults, poor dietary quality is a risk factor for numerous chronic diseases. It is unclear how these various sleep domains influence adolescents' diets because prior population-based studies have not effectively manipulated sleep, did not include objective sleep measures, and had short follow-up times.

Objectives: The objectives of this study were to examine 1) how adolescent sleep characteristics relate to dietary quality; and 2) how delay in high school start times (which lengthened sleep duration) affects dietary quality over 2 y.

Methods: In the START study, adolescents (grades 9-11, n = 423) attending 5 high schools in the Minneapolis, Minnesota metropolitan area were annually assessed in 3 waves (2016-2018). At Baseline, all schools started "early" (07:30 or 07:45). From Follow-up 1 through Follow-up 2, 2 "policy change schools" shifted to later start times (to 08:20 and 08:50). Three "comparison schools" maintained their early start throughout. Sleep characteristics were measured with actigraphy. Mixed-effect regression models were used to examine cross-sectional and longitudinal associations of sleep characteristics with dietary quality, and school start time policy change with dietary quality change.

Results: Cross-sectionally, later sleep midpoint and onset were associated with dietary quality scores 1.6-1.7 lower (both P < 0.05). However, no prospective associations were observed between sleep characteristics and dietary quality in longitudinal models. Shifting to later school start time tended to be associated with a 2.4-point increase in dietary quality score (P = 0.09) at Follow-up 1, but was not associated with change in dietary quality scores at Follow-up 2 (P = 0.35).

Conclusions: High school students attending delayed-start schools maintained better dietary quality than students in comparison schools; however, differences were not statistically significant. Overall study findings highlight the complexity of the relation between sleep behavior and diet in adolescence.

Keywords: actigraphy; adolescence; diet; high school; school start times; sleep timing.

FIGURE 1

START substudy participant flowchart. ASA24, Automated Self-Administered 24-Hour.

FIGURE 2

Differences in mean total HEI-2015 scores between policy change and comparison schools over time after adjustment. Results of a mixed-effect regression model estimating effect of policy change on dietary quality over a 2-y study period. Model adjusted for biological sex, nonwhite race, free or reduced-price meal eligibility, and parent education with a random effect for student nested within school. HEI-2015 overall dietary quality score ranged from 0 to 100. Time: 1: Baseline; 2: Follow-up 1; 3: Follow-up 2. HEI-2015, Healthy Eating Index 2015.